Paper No. 247-4
Presentation Time: 2:15 PM
IMPROVING THE RECORD OF CENOZOIC ATMOSPHERIC CO2 WITH STOMATAL INDEX OF FOSSIL GINKGO LEAVES FROM NORTH AMERICA
A high-resolution record of atmospheric CO2 concentrations in the past is necessary for understanding the effects of future greenhouse events. The inverse relationship between the stomatal index (SI) of Ginkgo leaf cuticles and atmospheric CO2 levels, calibrated from greenhouse experiments and herbarium specimens, has been used to compile a record of CO2 from fossil Ginkgo leaves. Temporal resolution of that record has been limited by availability of suitably preserved leaf cuticles, but useful data can now be gained by joint back-scatter and secondary electron microscopic examinations of fossil impressions. This opens the possibility of a higher resolution record that resolves short-lived greenhouse spikes. For example, impressions of late Paleocene Ginkgo cranei from Almont, South Dakota, close in age to the Paleocene-Eocene Thermal Maximum, had SI of 6.39 ± 0.24 %, which corresponds to 1167 ppmv CO2 using the 2009 transfer function of Retallack. In contrast, Ginkgo adiantoides from the Oligocene (30 Ma) Lyons flora of Oregon had near-modern SI of 9.6 ± 0.16 %, corresponding to 362 ppmv. A sample of Ginkgo adiantoides from the middle Miocene (16.5 Ma) Musselshell flora of Idaho has SI of 7.23 ± 0.34 %, or 771 ppmv CO2, reflecting the start of a middle Miocene thermal maximum. This last result highlights the importance of understanding middle Miocene paleoclimate and vegetation as a guide to our future if CO2 concentrations pass such levels before the year 2100.